Re: pthread_cond_signal/broadcast: necessary to hold mutex?

[Tobias Nygren <tnn%NetBSD.org@localhost>]

On Mon, 23 Mar 2026 21:50:41 +0100
Thomas Klausner <wiz%netbsd.org@localhost> wrote:

> - Time for a bug report?
> - Any ideas where this requirement comes from?

The hardcopy of "DEC OSF/1 Guide to DECthreads" DEC p/n AA-Q2DPB-TK
printed in 1994 which I happen to still have in my possession states on
page 56 for pthread_cond_wait:

```
Call this routine after you have locked the mutex specified in /mutex/. The results of this routine are unpredictable without first locking the mutex.
```

This predates the first publication of pthreads in IEEE 1003.1c-1995.
The wording strongly suggest that you should lock the mutex but doesn't
explicitly forbid not doing so. I guess POSIX copied those semantics but
made them more clear, as standards people do.

I think it would be OK to
s/must be held/must be held for defined behaviour/
in our manpage.

-Tobias